Transducer element with antiresonant baffle



1967 J. v. BOUYOUCOS 3,337,842

TRANSDUCER ELEMENT WITH ANTI-RESONANT BAFFLE Filed June 28, 1965 lo TRANS- AMPLIFIE E F I? 24 O w |5 MEDIUM 0 0 O 12 Q 3| 33 so 32 34a INVENTOR JOHN v. souvoucos ZVJM/ W/Z FIG.4

United States Patent 3,337,842 TRANSDUCER ELEMENT WITH ANTI- RESONANT BAFFLE John V. Bouyoucos, Rochester, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed June 28, 1965, Ser. No. 467,797 Claims. (Cl. 340-8) This invention relates to an improved transducer element for large arrays for propagating sound unidirectionally under water at great submergence depths.

In many underwater sound applications, it is important to transmit a search light or unidirectional beam in which the major portion of the acoustic energy is propagated in one chosen direction only.

To achieve unidirectional acoustic radiation from a large array of transducer elements, several methods have been employed in the past. On the one hand, acoustic reflectors such as air-filled tubes or other highly compliant members have been employed to reflect to the forward direction any backward radiated energy from the array of acoustic sources. On the other hand, transducer elements have on occasion been mounted within air-filled housings, and adapted to the housing in such a manner that negligible acoustic force is transmitted to the housing structure. In closely packed arrays of such elements, little backward radiation occurs, as the housings, which form the back surface of the array, are essentially motionless.

Neither of the above methods is particularly suitable for deep submergence operation, as, for example, at depths in excess of 500 to 1000 fathoms, due to the practical difliculties of pressure equalizing the air-filled regions of the reflectors or housings to the high ambient pressure of the surrounding environment.

Other methods have been proposed for achieving unidirectional radiation at great submergence depths such as the use of volume arrays or end fire arrays which are phased in such a manner to project the acoustic energy in a single direction. However, the size and weight of such configurations is generally prohibitive, particularly at low frequencies.

The above limitations are overcome, in this invention, by an element structure including a transducer housing, having mounted to one end thereof a radiating member. Embodied Within and attached to the housing is an antiresonant mass-spring structure. This structure is antiresonant with respect to the housing at the center of the chosen frequency band of operation. At, or in the vicinity of, the anti-resonant frequency of the structure, the housing is caused to exhibit to external forces an impedance to motion far in excess of the impedancedue solely to the mass of the housing and its contents. This high impedance enables the housing to be practically motionless even in the presence of large driving forces on the radiating member. Thus, in a closely packed, large array of such transducer elements in whichthe radiating faces are oriented in one direction, the reduced housing motion enables the majority of the acoustic energy to be propagated in the said direction, with only that energy arising from diffraction, scattering, and the residual housing motion transmitted in a backward direction.

In addition, the individual housings may be made small enough and rigid enough so that they may be filled with a relatively compliant liquid which does not impede the motion of the radiating surface, but which enables the housing interior to be readily pressurized to the surrounding ambient pressure of the environment in which the array is placed.

Therefore, it is an object of this invention to provide an' improved transducer element having high-power, unidirectional capability at great submergence depths.

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tudinal axis, a first end plate aflixed to one end of the housing, a second end plate aflixed to the other end of the housing adapted to generate acoustic waves in the medium, an anti-resonant mass-spring structure resiliently mounted in the housing, means for equalizing the pressure within the housing to the pressure in the medium, and means for coupling energy to the second end plate to generate acoustic waves.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIGURE 1 is a block diagram of an underwater acoustic array;

FIGURE 2 shows nine transducer elements mounted in an acoustic signal generating array;

FIGURE 3 is a perspective view of one transducer element of the array shown in FIGURE 2; and

FIGURE 4 is a cross-sectional view of the element in FIGURE 3 along lines 44.

FIGURE 1, the block diagram, shows a plurality of hydroacoustic amplifiers 10, 10a, 10b coupling energy via couplings 11, 12, and 13 to three acoustic wave generating transducers 14' 15, and 16. A medium 17, in this instance seawater, is shown to the right of transducers 14, 15, and 16. In operation, a predetermined frequency of sound is generated and fed to the hydroacoustic amplifiers which in turn couple acoustic energy to the transducers 14, 15, and 16 through the couplings 11, 12, and 13; the energy is coupled to the medium 17 in an efiicient manner with a minimum of peripheric oscillations by a correct design of the impedance characteristics of said transducers as hereinafter explained in more detail.

FIGURE 2 shows in a somewhat schematic form a plurality of such transducers, four of which are designated as, 20, 21, 22, and 23 mounted on rigid backing 24- ready for immersion in seawater. The backing 24 in this instance contains the necessary equipment for generating the desired frequency and also includes the hydroacoustic amplifiers.

FIGURE 3 is a perspective view of one of the transducers shown in FIGURE 2, designed as 20 has a back plate 31, a front plate 32, and a cylindrical housing 33. Plate 32 has a circular portion designated as 34 that is called a bender plate which actually flexes to couple energy to a surrounding medium.

FIGURE 4, the cross-sectional view along lines 44 in FIGURE 3 shows the housing 33, the back plate of 31, and the front plate 32 incorporating the bender plate 34. It is to be understood that the housing and front and back plates are sealed to each other that the entire inner cavity generally designated as 40 may be filled with a liquid such as oil so that the entire structure may withstand the immense pressures found at the bottom of the ocean. A pressure equalization means is provided to allow the internal pressure of the transducer to adjust to that of the surrounding water. This includes a small passageway or capillary tube 26 connecting the internal volume of transducer 20 to a cylindrical member 27 sealed by a rubber diaphragm 28. Thus, the seawater pressure is transmitted throughout the liquid, no large hydrostatic pressure gradients exist within the transducer.

A drive shaft 41 is shown coupled to the bender plate 34 along the central axis of plate 34 and the drive shaft 41. It should be noted that the circular portion 34a, as shown in FIGURES 3 and 4, is in reality an annular groove cut deeply into end plate 32. An annular slot 42 is cut in the back of the bender plate 34, closely positioned to slot 34a so that motions of a drive shaft 41 coupled to the bender plate caused it to oscillate back and forth, in this instance from left to right along axis 43. A member 44 is shown mounted through the back plate 31 for guiding the drive shaft 41. An ring 45 is held about the shaft 41 by a groove therein to prevent leakage of oil back and forth out of the transducer.

An anti-resonant mass 47 of generally cylindrical shape is mounted by resilient means 48, 49, 50, and 51 so that it may move along axis 43 in an oscillatory fashion. The resilient means 48 and 49 are springs under tension or compression and resilient members 50, 51 are then 90 angles afiixed to housing 33 and to the mass 47. The hydroacoustic amplifier shown in FIGURE 1, and designated as 10 would be coupled to the left end of drive shaft 41 but is not shown for the sake of convenience. It is to be further understood that in operation the transducer would be filled with oil but it has been left out for the sake of clarity in the drawing.

It can be shown by mathematical analysis that for maximum effectiveness of the system the mass of the antiresonant structure should be as much of the total of the transducer mass as possible. This sets certain design limitations since the housing must be designed as rigid as possible to contain the acoustic pressures generated in the compliant liquid due to bender plate motion.

If the mass of the transducer is M then the total mass is equal to:

M =the housing mass M =the first end plate mass M =the second end plate mass M =the anti-resonant mass M =the pressure equalizing means mass M =the energy coupling means mass In selecting the values for the above masses, it is desirable to make M as large a portion of the whole as possible. The limiting value is reached where the housing would cease to be strong enough to support the transducer and to operate properly.

For maximum power transfer to the medium, and to maximize the unidirectional property of the array, the anti-resonance frequency of the structure 47 comprising mass 47 and springs 48, 49, 50 and 51 should equal the resonant frequency of bender plate 34, as mass loaded by drive shaft 41 and the radiation load, with both said anti-resonant and resonant frequencies corresponding to the driven frequency.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. An improved transducer for generating acoustic waves in a medium, comprising:

(a) a housing having a longitudinal axis;

(b) an end plate affixed to said housing adapted to generate acoustic waves in said medium;

(c) a mass resiliently mounted to said housing, said mass and resilient mounting means providing an anti-resonant structure with respect to said housing;

(d) liquid means for equalizing the pressure within said housing to the pressure in said medium; and

(e) means for coupling energy to said end to generate acoustic waves.

2. An improved transducer for generating acoustic waves in a medium, comprising:

(a) a housing having a longitudinal axis;

(b) an end plate affixed to said housing adapted to generate acoustic waves in said medium;

(0) a mass resiliently mounted to said housing, said mass and resilient mounting means providing an anti-resonant structure with respect to said housing;

(d) liquid meansfor equalizing the pressure within said housing to the pressure in said medium; and

(e) means for coupling energy to said end plate to generate acoustic waves.

3. An improved transducer for generating acoustic waves in a medium, comprising:

(a) a hollow housing having a longitudinal axis;

(b) a first end plate affixed to one end of said housing;

(c) a mass resiliently mounted to said housing, said mass and resilient mounting means providing an antiresonant structure with respect to said housing.

(d) liquid means for equalizing the pressure within said housing to the pressure in said medium; and (e) means for coupling energy to said second end plate to generate acoustic waves.

4. An improved transducer for generating acoustic waves in a medium, comprising:

(a) a hollow housing having a longitudinal axis;

(b) a first end plate affixed to one end of said housing;

(c) a second end plate afl ixed to the other end of said housing adapted to generate acoustic waves in said medium;

(d) a mass resiliently mounted to said housing, said mass and resilient mounting means providing an anti-resonant structure with respect to said housing;

(e) liquid means for equalizing the pressure within said housing in the pressure in said medium; and

(f) means, including a hydroacoustic amplifier, for coupling energy to said second end .plate to generate acoustic waves.

5. An improved transducer for generating acoustic waves in a medium, comprising:

(a) a cylindrical housing having a first longitudinal axis and having first and second open ends;

(b) a first end plate affixed to one of said ends;

(c) a second end plate afiixed to the other of said ends adapted to generate acoustic waves in said medium;

(d) a mass evenly distributed about a second longitudinal axis resiliently mounted to said housing, said mass and resilient means providing an anti-resonant structure with respect to said housing, said first and second longitudinal axis being substantially coaligned;

(e) liquid means for equalizing the pressure within said housing to the pressure in said medium; and (f) means for coupling energy to said second end plate to generate acoustic waves.

6. An improved transducer for generating acoustic waves in a medium, comprising:

(a) a cylindrical housing having a first longitudinal axis and having first and second open ends;

(b) a first end plate affixed to one of said ends;

(c) a second end plate afiixed to the other of said ends adapted to generate acoustic waves in said medium;

(d) a mass evently distributed about a second longitudinal axis resiliently mounted to said housing, said mass and resilient means providing an anti-resonant structure with respect to said housing, said first and second longitudinal axes being substantially coaligned;

(e) liquid means for equalizing the pressure within said housing to the pressure in said medium; and (f) means including a hydroacoustic amplifier coupled between said first end plate and said second end plate for coupling energy to said second end plate and generate acoustic waves.

6 7. An improved transducer for generating acoustic (a) a housing having an axis and having first and waves in a medium, comprising: second ends;

(a) a hollow cylindrical housing having a longitudinal (b) a first end member in contact with said medium axis and having first and second open ends; mounted on one of said ends; (b) a first end plate affixed to said first end; 5 (c) a second end member mounted on the other of (c) a second end plate including a bender plate affixed said ends;

to said second end plate adapted to generate acoustic (-d) drive means passing through said second end memwaves in said medium; ber along said axis to said first end member to gener- (d) ahollow cylindrical mass resilienty mounted -to and ate acoustic waves in said medium in a given frecoaxially aligned with said housing, said mass and requency range; silient means providing an antiresonant structure with (e) a pressure sensitive means in said medium mounted respect to said housing; on said housing and operable through said housing (e) liquid means for equalizing the pressure within providing pressure compensation for said transducer;

said housing to the pressure in said medium; and and (f) means for coupling energy to said bender plate to (f) a liquid filling said housing and said sensitive generate acoustic waves. means for evenly distributing ambient pressure con- 8. In the transducer of claim 5 wherein the total mass, ditions throughout said transducer, said mass being M of the transducer is given 'by the formula anti-resonant at said given frequency range.

, 10. The transducer of claim 9 wherein said mass is at h MT MI+MZ+M3+M4+M5+MS least one-third the total mass of the transducer. were M =the housing mass References Cited M2=the first end P1ate mass UNITED STATES PATENTS Mg=the second end plate mass M =the mass of the resiliently mounted mass and the 2 16O4'693 10/1926 Hecht et resilient means 3,005,974 10/1961 Northrup et a1. 340-14 X M =the pressure equalizing means mass 3,187,300 6/1965 Brate 340 8 M =the energy coupling means mass 3,205,476 9/1965 Massa 34O8 the design characteristic that M is at least one-third of RODNEY D, BENNETT, Primary Examiner,

9. An improved transducer for generating acoustic CHESTER JUSTUS Exammer' waves in a water medium, comprising: J. P. MORRIS, Assistant Examiner. 

1. AN IMPROVED TRANSDUCER FOR GENERATING ACOUSTIC WAVES IN A MEDIUM, COMPRISING: (A) A HOUSING HAVING A LONGITUDINAL AXIS; (B) AN END PLATE AFFIXED TO SAID HOUSING ADATED TO GENERATE ACOUSTIC WAVES IN SAID MEDIUM; (C) A MASS RESILIENTLY MOUNTED TO SAID HOUSING, SAID MASS AND RESILIENT MOUNTING MEANS PROVIDING AN ANTI-RESONANT STRUCTURE WITH RESPECT TO SAID HOUSING; (D) LIQUID MEANS FOR EQUALIZING THE PRESSURE WITHIN SAID HOUSING TO THE PRESSURE IN SAID MEDIUM; AND (E) MEANS FOR COUPLING ENERGY TO SAID END TO GENERATE ACOUSTIC WAVES. 